Ultrasonic pulse echo method can be used to measure the pressure distribution between mechanical joints,but the measurement accuracyis affected by interface contact conditions,such as pressure loading history,surface roughness,contact medium,etc.According to ultrasonic propagation mechanism at the contact interface,the relationship model between the echo energy coefficient of the contact interface and the interface contact pressure was obtained.An ultrasonic testing system was set up,test pieces with different surface roughness were processed,and different kinds of lubricating media were prepared,and then pressure loading tests were carried out on the test pieces with different contact conditions.Curves of the echo energy coefficient of the joint surface changing with pressure was obtained.The results show that the curve obtained during the first loading process is obviously different from the last few loading,and the curves gradually coincide during cyclic loading.The contact surface with large roughness has large echo energy coefficient under the same contact pressure.When the contact medium has different material properties and interacts with surfaces of different roughness,the echo energy coefficient is also different at the same pressure.The research shows that the load history,contact surface morphology,and contact medium are the main factors affecting the propagation of ultrasound at the contact interface.The research results have reference value for the accurate measurement of the pressure distribution between mechanical joints.